Relationship between variations in cardiac output and end-tidal CO2 after phenylephrine infusion in anaesthetised patients

Subjects voluntarily hyperventilated for 10 breaths. A dynamic end-tidal forcing technique manipulated inspired gases to hold end-tidal CO2-O2 tensions at normal values during the voluntary ventilation period and the postvoluntary ventilation recovery period when the subjects returned to spontaneous breathing. Six of the seven subjects studied exhibited a hyperpnea during the recovery period. Although intersubject and intrasubject variations were evident, the average response for 30 experiments in the six subjects was characterized by an initial drop to 32% of the hyperventilation magnitude followed by an exponential-like decrease with a time constant of 22 s. This recovery period response is consistent with theoretical properties of neural network and physical oscillators where there is a persistence in the amplitude response after the removal of the stimulus. Thus, such oscillator properties may govern the respiratory center behavior in man. Furthermore, since isocapnic voluntary ventilation increases cardiac output, the recovery period response may be a consequence of cardiodynamic hyperpnea.

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IMPACT OF LARGE CHANGES IN MINUTE VENTILATION ON END TIDAL CO2 DURING CONTROLLED LOW CARDIAC OUTPUT IN SWINE

Critical Care Medicine ◽

10.1097/00003246-199304001-00235 ◽

1993 ◽

Vol 21 (Supplement) ◽

pp. S250 ◽

Cited By ~ 1

Author(s):

Jay L Falk ◽

A Idris ◽

K DelDuca ◽

D OʼBrien ◽

R Melker ◽

...

Keyword(s):

Cardiac Output ◽

Minute Ventilation ◽

Low Cardiac Output ◽

End Tidal ◽

End Tidal Co2

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Cyclic hypoxic pulmonary vasoconstriction induced by concomitant carbon dioxide changes

Journal of Applied Physiology ◽

10.1152/jappl.1976.41.4.466 ◽

1976 ◽

Vol 41 (4) ◽

pp. 466-469 ◽

Cited By ~ 41

Author(s):

J. L. Benumof ◽

J. M. Mathers ◽

E. A. Wahrenbrock

Keyword(s):

Blood Flow ◽

Cardiac Output ◽

Regional Blood Flow ◽

Hypoxic Pulmonary Vasoconstriction ◽

Lower Lobe ◽

Co2 Concentration ◽

Hypoxic Area ◽

Pulmonary Vasoconstriction ◽

End Tidal ◽

End Tidal Co2

We examined the stability of acute lobar hypoxic pulmonary vasoconstriction. In 12 mongrel dogs the left lower lobe (LLL) was selectively ventilated with a constant minute molume with nitrogen and the electromagnetically measured fraction of the cardiac output perfusing the LLL and the LLL end-tidal CO2 concentration were observed for 1 h. We found that both the fraction of the cardiac output perfusing the LLL and the LLL end-tidal CO2 concentration initially decreased during LLL hypoxia and then oxcillated in a progressively damped fashion. When LLL end-tidal CO2 was kept constant by CO2 infusion during LLL hypoxia or when LLL hypoxia was induced by LLL atelectasis, no oscillations were observed. We conclude that if minute ventilation of a hypoxic area of lung is kept constant, then decreased regional blood flow decreases regional alveolar PCO2. As a consequence of these two opposinginfluences, blood flow to an acutely hypoxic area will be oscillatory.

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